1. Field of the Invention
This invention relates to integrated circuit structures. More particularly, this invention relates to a chucking structure useful for securing a semiconductor substrate to a substrate support during the formation and/or testing of an integrated circuit structure thereon, particularly in a vacuum environment.
2. Description of the Related Art
In the construction of integrated circuit structures on semiconductor substrates, the substrate is normally secured to an underlying substrate support in a vacuum environment by one of two conventional means, an edge gripping mechanical clamping structure, or an electrostatic chuck.
While edge gripping mechanical clamping structures keep the substrate from slipping, i.e. keep the substrate from horizontally sliding or moving on the substrate support, such an edge gripping mechanical clamping structure does not flatten the substrate to the underlying substrate support. Since some substrates, such as single crystal silicon semiconductor wafers, are formed slightly convex, it is very important that the substrate be flattened against the substrate support during processing of the substrate, to prevent or inhibit problems with, for example, photolithography processing on the surface of the substrate.
However, the primary disadvantage of edge gripping or clamping mechanisms is that they may cause damage to the substrate during the exercise of mechanical force on the substrate. Furthermore, additional hardware is usually required to insert and extract the substrate to and from the clamping mechanism.
While the problems of mechanical damage to the substrate and positioning the substrate to lie flat on the substrate support are not encountered as often when using an electrostatic chucking mechanism, there are many disadvantages distinctive to electrostatic chucks as well, including high voltage requirements, dangerous stored energy, the need for complex mechanical and electrical apparatus, premature release of the substrate in vacuum, dependance on the substrate for chucking effectiveness, expense of the equipment, large size (both in weight (heavy) and dimensions. (wide)), particle generation, and decreased substrate throughput.
It would, therefore, be desirable to provide a substrate retention mechanism which would permit a substrate to be secured to a substrate support without encountering the problems just discussed relating to either mechanical clamping of the substrate to the substrate support or electrostatic clamping of the substrate to the substrate support.
Autumn et al., in an article entitled xe2x80x9cADHESIVE FORCE OF A SINGLE GECKO FOOT-HAIRxe2x80x9d, which appeared in volume 405 of Nature on Jun. 8, 2000, at pages 681-685, reported that a gecko lizard""s foot, such as shown, for example, at 2 in prior art FIG. 1, has nearly five hundred thousand keratinous hairs or setae, such as shown, for example, at 4 in prior art FIG. 2. Each such seta is said to be only about one-tenth the diameter of a human hair. The authors further state that each seta has, at its terminus, hundreds of projections or split ends, each terminating in 0.2-0.5 xcexcm spatula-shaped structures such as shown, for example, at 6 in prior art FIG. 3. The authors indicate that the setae of the gecko foot apparently adhere to surfaces by Van der Waals forces, and that individual setae were measured and each seta was found to exert a force of about 194xc2x125 xcexcNewtons (xcexcN).
Subsequently, an unsigned article appeared in the August, 2000 MRS Bulletin entitled xe2x80x9cGECKO FOOT HAIR RESEARCH FEEDS ADHESIVE DEVELOPMENTSxe2x80x9d which indicated that measurements of the force of individual foot hairs (setae) of geckos have resulted in estimates of a Van der Waals force ranging from about 40 xcexcN to 400 xcexcN per seta.
An article by Glennda Chui appearing in the San Jose Mercury News on Jun. 13, 2000, entitled xe2x80x9cCLIMBING THE WALLS GECKOS SECRET OFFERS POTENTIAL FOR ADVANCES IN ADHESIVES, ROBOTICS AND CHIP-MAKINGxe2x80x9d, also described the forces developed by the hairs on a gecko""s foot and then, after commenting upon the possible use of this discovery in forming new dry adhesives, further suggested the use of such technology in moving silicon chips and other electronic components around during manufacture without risk of scratching.
A process and apparatus is disclosed capable of removably adhering a semiconductor substrate to a substrate support in a sub-atmospheric environment using a plurality of individual fibers, each mounted at one end adjacent the substrate support. When the portions of the fiber adjacent the loose fiber ends are each brought into contact with the under surface of the substrate, Van der Waals forces are exerted between the substrate and the fibers to urge the substrate toward the underlying substrate support. In a preferred embodiment, the substrate and portions of the fiber adjacent the loose fiber ends are first vertically brought into physical contact with one another, and then a horizontal force is applied to horizontally move, with respect to one another, the substrate and the portions of the fibers adjacent the loose fiber ends. After application of the horizontal force, a vertical force is applied between the substrate and the fibers of sufficient strength to urge the substrate and the fibers away from one another without breaking contact between the substrate and the portions of the fiber adjacent the fiber ends to thereby place tension on the substrate to urge the substrate to lie flat against the underlying substrate support.